In Ethernet (registered trademark), each device is identified by a media access control (MAC) address. A MAC address is a unique address of each device. In Ethernet, a frame processing device configured to perform layer 2 transfer processing performs frame transfer processing, based on a MAC address included in a frame. In Ethernet, a frame processing device that performs layer 2 transfer processing is, for example, a layer 2 switch.
When a layer 2 switch receives a frame, the layer 2 switch associates the transmission source MAC address of the frame and the reception port of the frame with each other and learns an address. The learned MAC address is associated with the reception port when the MAC address has been learned, and is registered in a MAC address table. In transferring a frame, the layer 2 switch performs a search for the destination MAC address of the frame in the MAC address table and outputs, if there is registration of the destination MAC address, the frame from a port associated therewith in the MAC address table.
A frame the destination MAC address of which has been learned, that is, a frame the destination MAC address of which is registered in the MAC address table, will be hereinafter referred to as a learned frame. Also, a frame the destination MAC address of which is un-learned, that is, a frame the destination MAC address of which is not registered in the MAC address table, will be hereinafter referred to as an un-learned frame.
In frame transfer processing of Ethernet, an un-learned frame undergoes flooding processing. Flooding processing is processing of copying a frame and outputting copy frames of the frame from all of ports other than the reception port thereof. For an un-learned frame, an output port thereof is not known, and therefore, the un-learned frame is output from all of ports other than the reception port, and thus, reaches a device of the destination MAC address.
On the other hand, for a learned frame, an output port thereof is known, the frame is not copied and is output from the output port.
FIG. 1 is a diagram illustrating an example of frame transfer processing of a layer 2 switch. A layer 2 switch P1 includes a learning determination unit P11, a frame copy processing unit P12, a buffer P13, a unicast transfer processing unit P14, and a MAC address table P51.
When a frame is input, the learning determination unit P11 performs a search for the destination MAC address of the frame in the MAC address table P51 and determines whether the frame is a learned frame or an un-learned frame. If the input frame is a learned frame, the learning determination unit P11 outputs the input frame to the buffer P13. If the input frame is an un-learned frame, the learning determination unit P11 outputs the input frame to the frame copy processing unit P12.
When the frame is input from the learning determination unit P11, the frame copy processing unit P12 generates copy frames of the frame of a number corresponding to the number of ports and outputs the copy frames to the buffer P13. Note that frames that are output to the buffer P13 by the frame copy processing unit P12 include an original frame but, for convenience, will be collectively referred to as copy frames.
The buffer P13 is a first-in-first-out (FIFO) queue. The unicast transfer processing unit P14 reads a frame from the buffer P13 and outputs the frame to the output port of the frame.
Japanese Laid-open Patent Publication No. 11-122303 and Japanese Laid-open Patent Publication No. 2006-279820 discusses related art.